Andrew Kuchling <amk at amk.ca> added the comment:
Ignore my previous idea of a problem with the dictionary iterator; it's just
pickling many dictionaries with the same set of keys. It seems like pickling
works after all, but it's just much slower; for me it takes 18sec to pickle to a
file, but 176 sec to pickle to a StringIO. The resulting pickle output seems to
exactly match the output that's written directly to a file, so I don't think
there's an actual bug here, just some very bad performance in StringIO.write().
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PyPy bug tracker <tracker at bugs.pypy.org>
<https://bugs.pypy.org/issue979>
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